The AFFIRM Study will compare whether optimized antiarrhythmic drug therapy administered in an attempt to maintain normal sinus rhythm has an impact on total mortality when compared to optimized therapy which merely controls the heart rate of the main pumping chambers during atrial fibrillation. The study will be analyzed on an intent-to-treat basis. The hypothesis is that in patients with atrial fibrillation, total mortality with primary therapy intended to maintain sinus rhythm is equal to total mortality with primary therapy intended to control heart rate. Because stroke is such an important endpoint, composite endpoints will include 1) total mortality and disabling stroke and disabling anoxic encephalopathy; 2) total mortality, disabling stroke, or anoxic encephalopathy, major bleeding, and cardiac arrest. A third objective is to ascertain the cost of each therapy. There are 200 sites participating in the main trial which will run from 5/96-10/99 with the goal of 5000 enrolled patients.